OK Need Serious Advice Major Engine Problems

ok so i recently purchased a 96 sunfire 2.2L and it just started over heating one day. and when i say overheat i mean overrrrrrrrrheat. but i found out that it wont over heat when i leave the heater off. its like my temperature switch on my climate control controls my engines temperature ha ha. okay but seriously ive replaced the water pump put in a new thermostat and flush out the heater core. and it still overheats only when i turn on the heater. now im usally a honda guy but i got this thing for a steal from a friend of mine and its a great car to go to work with good gas mileage. so anything else yall think could be causing this to happen???

Weird situation, but when you do have heat on does inside car get hot as well?

Does defrost setting do same thing?


Even if vents stuck closed would never cause car to overheat, not when you state oevrheat can you confirm engine is hot( through some water on it, if evaporates immediatly means overheating ) or is it just gauge on dash as it maybe faulty. Could be a sensor as well.

well if the motor is idleing it blows out cold air. but if im moving it definatly is very hot air coming out. and if i have the defrost on it does the same thing. anything dealing with heat coming out of any of my vents it overheats. yes engine is definatly overheating it dumps all the rad fluid on the ground. and even comes out of the top of the rad cap. so yeah its definatly really overheating not a faulty gauge. i thought it would have been the heater core but when i manually ran water through it it went right through. any more suggestions??? like i said im not used to these gm motors??? and ive definatly never heard of anything like this happing. but i tell you what its freezing outside and i need to be able to run my heater : )!

i had a cavalier and the heater never worked so i waited until the engine heated up and turned it on vent and the heat of the engine would blow into my car.

the heater works its just when i turn the heater on it for some reason makes the engine overheat???

I wonder if you may have a blockage in system causing it to not circulate fluids and thus overheat in same area, as coolant is ment to flow throughout system.

Not sure how you could test for blockage.

thats what i dont understand it does perfectly fine as long as the heat is not on. and the only deference is that the water then has to flow through the heater core when you turn the heat on but i checked and flushed that and still the same thing. so... im still confussed. i just dont want to put in the shop and them fix the wrong part and me have to pay a lot of money and the problem still not be fixed. so anybody else know what could be going on here????

Does the fan on radiator turn on?????? It maybe bad

yeah fan turns on fine. i checked it throughly and its working great

Have you started heat in car and open hood to verify fan is turning when heater on?

As well, have you had your antifreeze checked for temperature ( aka -40degrees celcius ) If car more full of water, usually heaters do not work well and evaporates through engine

yeah ive definatly seen the fan cut on. its got the 50/50 mixture of dex-cool aproved antifreeze. i will try to verify the actuall temp of the fluid

Check under car and see if catalitic converter may be plugged.

what do you mean by plugged???

When a catalitic converter gets plugged, it can get RED and very very hot, restricting exhaust from exiting through muffler system.

why would that cause it to overheat only when the heater is on though??? oh and today when i was on the intersate i turned on the heater and it did fine but as soon as i dropped below like 65 it started making the engine overheat so plug that into the equation. and tell me what you think???

Is the equation

>= 65 heat good engine not over heat with heat on,
< 65 engine overheats with heat on

car must be possesd as it is doing everything in reverse diagnostics.

Yeah thats what its doing. It's crazy i can't figure it out. It's the strangest thang I've ever heard of???

Yeah thats what its doing. It's crazy i can't figure it out. It's the strangest thang I've ever heard of???
Well are there any updates as to what the problem is?

nothing yet??? anybody else have any ideas??

nothing yet??? anybody else have any ideas?? send a private message to richtazz over in Grand Prix forum and run it by him. No disrespect to any people here but he is a Gm parts guy and seems very knowledgeable. bnaylor is also good but he`s into Gp`s. let us know how you make out Good Luck

Sounds like you have an air pocket in the cooling system. The heater core in your car is one of the highest points in the cooling system, so that is where the air settles when you shut off the car. When you turn on the heater, coolant pushes the air pocket into the engine, where it's getting staying in the cylinder head causing the engine to rapidly overheat. There should be a coolant bleeder valve on the t-stat housing that will help in bleeding the air out. A good repair manual will have the proceedure in it. Getting the air out is a pain in the a$$, but that's the problem you are having.